Costs and benefits of compliance: New Zealand drinking water standards
Annual Conference
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In New Zealand, water suppliers are required to take all practicable steps to comply with the Drinking Water Standards 2005 (DWSNZ), published by the Ministry of Health (MoH). For many smaller communities, the costs of upgrading water supply infrastructure to comply with DWSNZ are substantial, but water suppliers do not estimate the benefits.
In this paper we propose a method for calculating the public health benefits associated with DWSNZ compliance. Our calculations suggest that for a catchment with high protozoal risk, the benefit cost ratio for upgrading to a compliant plant could be between 0.5 and 7.1. Furthermore, the number of illnesses could be reduced by 100 times.
The benefits of protozoal compliance due to cost of illness avoided depend on the number of infectious Cryptosporidium oocysts in the source water. We recommend that water suppliers are familiar with their catchment risks in order to understand the level of public health risks inherent in their water supplies.